The present invention relates to a semiconductor storage device which can be used as a substitute for the conventional small-size magnetic disk device.
The conventional semiconductor disk storage disclosed by JP-A-2-81398 includes a non-volatile semiconductor memory which has a certain memory capacity and a volatile memory which has the same memory capacity as the non-volatile memory. In the disclosed semiconductor disk storage, a volatile memory having a high writing speed is generally used. At the time of the turn-off of a power supply, all data in the volatile memory are transferred to the non-volatile memory. Thereby, the preservation of data upon turn-off of the power supply and the improvement of an operating speed at the time of normal operation are implemented.
This prior art supposes a storage device for a large-size computer and gives the miniaturization no sufficient consideration. Namely, 3.5-inch, 2.5-inch and 1.8-inch hard disk devices are used in recent small-size work stations, personal computers or the like and semiconductor storage devices are also required to cope with such sizes.
The identity in capacity between the volatile memory and the non-volatile or flash memory in the above-mentioned prior art means the need of cache memories the number of which is substantially the same as that of the flash memories. Therefore, it is difficult to miniaturize a semiconductor disk device to a size on the same order as that of the small-size hard disk device.